Corona discharge

• When an uncharged body is brought near a charged body having sharp corners there is large number of charges at the corners. Due to induction, they induce large number of opposite charges. This creates a very strong Electric field between them. Finally the dielectric strength breaks-down and there is fast flow of charges. This Spray of charges by spiked object is called Corona discharge. 
• The lightening arrester work on the principles of Corona discharge where the charge pass through conductor of arrester, and the buildings are saved 

The working of a rocket is based on the principle of

 (a) Elasticity 

(b) Kepler's law  

(c) Newton's law of gravitation 

(d) Conservation of momentum.

THE RIGHT ANSWER IS

(d) Conservation of momentum.

REFRACTION OF LIGHT

 

Change in momentum is given by

(a) Force x Mass 

(b) Force x Time 

(c) Force x Velocity 

(d) Force x Distance. 

THE RIGHT ANSWER IS

(b) Force x Time 

The units of Impulse are same as that of

 

(a) Energy 

(b) Linear momentum 

(c) Velocity 

(d) Power. 

RIGHT ANSWER IS 

(b) Linear momentum 

Rules for writing units

1) The symbol of a unit, which is not named after a person, is written in lower letter (small letter). 

Eg: metre (m) kilogram (kg) 

2) The symbol of a unit, which is named after a person, is written with a capital initial letter. 

Eg: newton (N), kelvin (K) 

3) Full name of a unit, even if it is named after a person is written with a lower initial letter. 

Eg: newton, kelvin. 

4) A compound unit formed by multiplication of two or more units is written after putting a dot or leaving a space between the two symbols.

Eg: newton metre — N.m or N m. 

5) A unit in its short form is never written in plural.